Megadams: Pros, Cons, and Consequences

 

Humans have diverted water from its natural channels throughout history.  Remains of water storage dams are found in Jordan, Egypt and other parts of the Middle East dating back to at least 3000 BC., 5000 years ago.  

 

However, the era of large dams or "megadams" was ushered in by the Bureau of Reclamation Act of 1902.  “Large dams” are officially defined by the World Commission on Dams as having heights greater than 15 m, or reservoir capacities greater than 3,000,000 cu meters.”  By these criteria, there are 45,000 large dams world wide spead over 150 countries, and their combined reservoirs cover an area larger than the country of France.  Of these dams, about half are used exclusively or primarily for irrigation, accounting for 271 million irrigated hectares (271 sq km? If 1 ha=10E4 m).

 

Even the biggest and most prominent of the U.S. dams and their associated lakes (Grand Coulee, Hoover (221 m high), Glen Canyon, 215 m high) are dwarfed by a number of other dams around the world (e.g., Owen Falls, Uganda; Kariba, Zimbabwe/Zambia; Bratsk, USSR; High Aswan, Egypt, Akosombo, Ghana;and, potentially, Rogun in the USSR, or Three Gorges, China, and others.) 

 

Look first at dams by height:

 

Rank No. 

Name of Dams 

Country

Height (m) 

Year Completed 

1

2

3

4

5

6

7

8

9

10 

Rogun

Nurek

Grand Dixence

Inguri

Boruca

Vaiont

Tehri

Chicoasen

Kishau

Guavio 

USSR

USSR

Switzerland

USSR

Costa Rica

Italy

India

Mexico

India

Columbia 

335

300

285

272

267

262

261

261

253

246 

____

1980

1961

1980

1990

1961

1990

1980

1995

1989 

Copyright © 1997 - Department of Irrigation Engineering

www.eng.ku.ac.th/~irre/E10LARGE.HTM  

 


Top 10 Largest Storage Dams in the World 


Rank No.

Name of Dam

Country

Storage Capacity (MCM) 

Year Completed 

1

2

3

4

5

6

7

8

9

10

Owen Falls

Kariba

Bratsk

Aswan, High

Akosombo

Daniel Johnson

Guri (Raul Leoni)

Krasnoyarsk

Bennett W.A.C.

Zeya

Uganda

Zimbabwe/Zambia

USSR

Egypt

Ghana

Canada

Venezuela

USSR

Canada

USSR

204,800

180,600

169,270

168,900

148,000

141,852

138,000

73,300

70,309

68,400

1954

1959

1964

1970

1965

1968

1986

1967

1967

1978


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Last updated 6 March 1998 by fengvwv@nontri.ku.ac.th

Copyright © 1997 - Department of Irrigation Engineering

 

 

Rank No.

Name of Dam

Country

Storage Capacity (MCM) 

Year Completed 

1

2

3

4

5

6

7

8

9

10

Owen Falls

Kariba

Bratsk

Aswan, High

Akosombo

Daniel Johnson

Guri (Raul Leoni)

Krasnoyarsk

Bennett W.A.C.

Zeya

             Uganda

Zimbabwe/Zambia

USSR

Egypt

Ghana

Canada

Venezuela

USSR

Canada

USSR

204,800

180,600

169,270

168,900

148,000

141,852

138,000

73,300

70,309

68,400

1954

1959

1964

1970

1965

1968

1986

1967

1967

1978

Copyright © 1997 - Department of Irrigation Engineering

www.eng.ku.ac.th/~irre/E10LARGE.HTM  

 

 

 

As an aside discovered preparing this talk, Syncrude Tailings Dam in Canada is currently ranked number one by volume of construction material at 706,320,000 cubic yards (540,000,000 cubic meters). These are mine tailings so the more they mine and add to the tailings the larger the structure will grow. In contrast, Hoover Dam contains 3,250,000 cubic yards (2,600,000 cubic meters) of concrete, which is much less. Hoover Dam is solid concrete and it was designed specifically to be used as a dam, whereas, the Syncrude Tailings is the piled up dirt left over from mining operations. Although the material is compacted and otherwise treated to make a stable structure it relies on volume of material to hold water back. Hoover Dam relies not only on volume of material but the strength of that material.


 

 

Benefits of dams

 

Water storage

 

Flood control

Floods affected the lives of 65 million people between 1972 and 1996.

Irrigation

Dams contribute to 12-16% of world food production.

Electrical Power Generation

19% of the worlds total electricy supply, in 150 countries.  24 countries depend on dams for 90% of their power supply.

Industrialization

 

Increased croplands

 

Improved navigation

Stabilized annual flows

Improved domestic water availability

In 1990, over a billion people had access to less than the minimum required of 50 litres per person per day.

Recreation

Fishing cab be improved esp. in lakes but also in rivers with introduced species, leisure (e.g., boating on lakes, extended rafting season on the Colorado River)

Ecological

Increased riparian vegetation if dam discharges are steady

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To quote from “Dams and Development: A new framework for decision making” The Report of the World Commission on Dams, 2000:

“During the 20th century, large dams emerged as one of the most significant and visible tools for the management of water resources. The more than 45 000 large dams around the world have played an important role in helping communities and economies harness water resources for food production, energy generation, flood control and domestic use. Current estimates suggest that some 30–40% of irrigated land worldwide now relies on dams and that dams generate 19% of world electricity.

From the 1930s to the 1970s, the construction of large dams became – in the eyes of many –synonymous with development and economic progress. Viewed as symbols of modernisation and humanityęs ability to harness nature, dam construction accelerated dramatically. This trend peaked in the 1970s, when on average two or three large dams were commissioned each day somewhere in the world.

While the immediate benefits were widely believed sufficient to justify the enormous investments made – total investment in large dams worldwide is estimated at more than $2 trillion – secondary and tertiary benefits were also often cited. These included food security considerations, local employment and skills development, rural electrification and the expansion of physical and social infrastructure such as roads and schools. The benefits were regarded as self-evident, while the construction and operational costs tended to be limited to economic and financial considerations that justified dams as a highly competitive option.”

 

(Image from The World Commission on Dams, www.dams.org)

 

 

Clearly, a major effect of any megadam is the impact on the preexisting ecological system. 

 

 

 

Kariba Dam, copyright M.D. Hutchinson

 

I’ve done a lot of work on the effects of Glen Canyon Dam on the ecology of the Colorado River, but that’s a relatively well known story to this audience. Peter Busack just returned from a journey that included a visit to Lake Kariba, pictured here, and the history and metaphorical lessons about this dam are so powerful that I’d like to use it in the context of this symposium instead of the cold, cry facts of the Glen Canyon Dam story.

 

Briefly, when this dam was completed in 1960, it was the largest man-made dam (lake/???)  ever built (Sue—Hoover Dam??).   The dam is 36.6 m high, with a thickness of over 24 m.  Ten million litres of water pass through the spillways each second.  At the end of 1958, the sluice gates were closed, and in 1963, the maximum lake level was reached.

 

 The lake is 220 km long, and in places up to 40 km wide; it provides electric power to both Zambia and Zimbabwe, and supports a thriving commercial fishing industry.  It has a potential for tourism that could benefit Zambia, including, supposedly, the Tonga People, whose traditional lands lie buried beneath the lake.

 

 

Fast areas of forest and scrub  on the Zambezi flood plain were indudated.  Thouseands of wild animals lost their habitats, and local villages had to be relocated.  The vegetation wasstrip-cleared and burnt, making the lake rich in chemicals from the fired wood. 

 

Now, for the mythology about cons and consequences.  The name Kariba refers to a rock which thrust out of the swirling water at the entrance of the gorge close to the dam wall site, now buried more than 100’ below the water surface.  In many local legends, this rock was regarded as the home of the great River god Nya-min-yami.  This god was rather powerful, as he caused anyone who ventured near to be sucked down for ever into the depths of the river.  When the Tonga people living in the valley heard that the great Zambezi River was to be blocked by a dam, they believed that it would anger Nya-min-yami so much that he would cause the water to boil and destroy the white man’s dam with floods.

 

??Coincidentally???, in 1957, a year into construction of the dam, the river rose to flood level and destroyed some equipment and the access roads.  The odds against another flood of the same size occurring the following year were about 1000:1.  But, guess what.  Just because events are rare, it doesn’t mean they can’t happen two years in a row.  In 1958 a flood 3 meters higher than the 1957 flood took out the access bridge, the coffer dam, and parts of the main wall.  Nya-min-yami recaptured the gorge with a flood of 16 million litres/second—a 10,000 year flood instead of the 1000-year flood of the previous year.  “Man eventually won the battle” and the dam finally opened in 1960.

 

Often, the change or destruction of the previous system is deemed to be “beneficial”, and that the anthrocentric economic advantages to humans would outweight the loss of wildlife and disturbance to indigenous peoples.  However, the lakes behind dams often submerge beautiful and historic areas, cover ancient artifacts, and can cause massive relocation of people who live along river banks. Often the displaced people are indigenous natives who are marginalized by the rapidly developing global economic culture.  In the case of the Kariba dam, 50,000 people of the Batonga tribe were forceably moved, not even knowing about electricity and possible benefits that it might bring them.  They were reluctant to leave their tribal lands, feared displeasing Nya-min-yami, and were forceably removed by trucks after holding ceremonies to honour their gods.  Schools and clinics were built in some of the new areas, and wells were drilled in some villages.  The villages that were located close to the water’s edge have prospered with the new fishing opportunities on the lake, but many villages in the higher sandy areas suffer from the loss of the rich alluvial soil and battle to produce crops.  The disruption of life was severe, and the compensation was minimal.

 

Meanwhile, as the dam began to dill, thousands of animals were being stranded on islands in the developing lake.  “Operation Noah” was instituted to raise money to buy boats and equipment for rescue and relocation of the animals.  The operation was frought with dangers ranging from submerged tree stumps that endangered the boats to concentrations of the deadly black mamba snakes on the islands.  There were heroic stories of mambas and rhinos being rescued (a total of 7000 animals over a lake that is 200 km long and at places 40 km wide).  But the stories of tragedy are ugly and despairing: monkeys, unable to swim, starving and too afraid of humans to allow themselves to be rescued, their skins then rotting in the water.  Smaller animals, reptiles and insects drowned.  It is an example of the anthropcentric view of the world that has prevailed during times long before megadams, but typified on a comprehensible scale by even the smallest of the megadams.

 

 

A fishing boom—probably temporary—resulted as the lake flormed because of the rich fertilizing effect of the chemicals from the strip clearance and burning.  A tiny sardine-like fish, the kapenta, eventually grew in commercially viable quantities and could be dried for easy distribution as a high protein food supplement where fish were hard to obtain.  The pressure has already increased on the kapenta supply so that tonnage is in danger of decline and licensing will have to be monitored and enforced.  Sportful game-fishing, for those who like it, is provided by tiger fish which flourish in the lake.

 

The Zambia Electricity Supply Company has established a project to address some of the environmental and social issues: road rehabilitation, provision of clean water, electrification, construction of schools, improved agricultural production, technical assistance, and health improvement.  The cost of this project is estimated at over $US12-million through the World Bank and Development Bank of Southern Africa.  The beneficiary community is expected to contribute 25% of the project cost (presumeably through manual labor and some raw materials?) and the government through the Rural Electrification Fund.

 

 

CONS OF DAMS

Ecological disruption

Fragmentation of 60% of the worlds rivers;

 

Disruption of movement of species (e.g., destruction of up to 75% of riparian bird species on the Colorado)

 

Destruction of riparian vegetation if discharges are irregular, e.g., peak-power of flood control types of operations; loss of beaches and marshes

Seepage and evaporation

15% for Nile system

Groundwater table effects

 

Sedimentation behind dams

 

Erosion downstream by sediment-starved waters

 

Flucuation vs. steady releases

Flucuations strand fish, reduce habitat for larval native fishes; deny access to tributaries;

Clogging of rivers by side-canyon floods

Peak floods required to clear channel may be eliminated

 

 

 

 

 

 

 

 

 

Dams and the associated lakes induce seismicity in previously aseismic regions.

 

Seepage and evaporation from the big lakes can be significant (e.g., ~15% for the Nile system), and groundwater levels can be affected. 

 

On a longer term, the consequences to the geologic and biologic systems are severe: sediment is deposited behind the dams, and so erosion is increased downstream. 

 

Failure of a dam could cause massive floods. 

 

Natural fertilizers are not replenished by annual floods, and the use of artificial fertilizers increases toxic minerals and salinity. These enter the food chain in potentially toxic levels.  Waste of human and nonhuman origins is concentrated by lack of drainage, in places leading to increase disease threats.  Downstream, where such contaminated water enters an ocean or sea, even the large bodies of water are affected, e.g., changes in the sardine and shrimp populations of the Mediterranean caused by the dams on the Nile. 

 

 

Thus, in an era where nearly every form of energy generation has pros and cons, the pros, cons, and consequences of big dams must be weighed against those of alternate energy sources.

 

CONSEQUENCES OF DAMS

 

The average large dam today is 35 years old.

 

Need for remediation

 

    ecological

 

    cultural

 

    economic

 

 

 

 

 

Note wording of “sustainable improvement of human welfare—bad choice of words.

“With these conflicts and pressures in mind, the World Commission on Dams began its work in May 1998. One of the Commissioners' first points of agreement was that dams are only a means to an end. What is that end? How central are the challenges that large dams set out to meet? And how well can they meet these challenges?

The WCD concluded that the 'end' that any project achieves must be the sustainable improvement of human welfare. This means a significant advance of human development on a basis that is economically viable, socially equitable and environmentally sustainable. If a large dam is the best way to achieve this goal, it deserves support. Where other options offer better solutions, they should be favoured over large dams. Thus the debate around dams challenges views of how societies develop and manage water resources in the broader context of development choices.

After more than two years of intense study, dialogue with those for and against large dams, and reflection, the Commission believes there can no longer be any justifiable doubt about five key points:

1.     Dams have made an important and significant contribution to human development, and the benefits derived from them have been considerable

2.     In too many cases an unacceptable and often unnecessary price has been paid to secure those benefits, especially in social and environmental terms, by people displaced, by communities downstream, by taxpayers and by the natural environment.

3.     Lack of equity in the distribution of benefits has called into question the value of many dams in meeting water and energy development needs when compared with the alternatives

4.     By bringing to the table all those whose rights are involved and who bear the risks associated with different options for water and energy resources development, the conditions for a positive resolution of competing interests and conflicts are created

5.     Negotiating outcomes will greatly improve the development effectiveness of water and energy projects by eliminating unfavourable projects at an early stage, and by offering as a choice only those options that key stakeholders agree represent the best ones to meet the needs in question

End quote”